1. Field of the Invention
The invention concerns a dryer section for drying a running web in a multi-cylinder dryer section of a paper making or board making machine It also concerns a process for drying such a web.
2. Related Publications
Modern, high-speed paper making or board making machines have a dryer section, e.g. in accordance with DE-PS 27 30 149, which is equivalent to U.S. Pat. No. 4,183,148. This includes a large number of web dryers, in the form of cylindrical drums of equal diameter, generally either 1.25 m, or 1.5 m or 1.8 m. The dryers are arranged in two rows, one above the other. The web moves over the dryers in series alternating from one row to the other. The dryers are each heated with steam. The first dryers in the series are used to heat up the wet web. They have a lower surface temperature than the succeeding dryers in the series. The temperatures of the dryers usually rise gradually in the direction of web travel. The dryer drive system is combined into groups. The web is guided so as to meander alternately from row to row through the dryer section. In the process, the running web wraps the dryers with approximately the same centri-angle.
FIG. 9 of U.S. Pat. No. 3,868,780, issued Mar. 4, 1975; and FIG. 4 of PCT International Application WO 88/06204, published Aug. 25, 1988, also disclose drying sections wherein the dryer cylinders are grouped into groups. Both of these disclosures show groups of drying cylinders of equal size.